1. Field of the Invention
This application relates generally to processes for depositing metal containing films. Certain embodiments relate to processes for manufacturing metal containing thin films by atomic layer deposition using volatile metal containing cyclopentadienyl compounds as source materials.
2. Description of the Related Art and Summary of the Invention
Atomic layer deposition (“ALD”) refers to vapor deposition-type methods in which a material, typically a thin film, is deposited on a substrate from vapor phase reactants. It is based on sequential self-saturating surface reactions. ALD is described in detail, for example, in U.S. Pat. Nos. 4,058,430 and 5,711,811, incorporated herein by reference.
According to the principles of ALD, the reactants (also referred to as “source chemicals” or “precursors”) are separated from each other, typically by inert gas, to prevent gas-phase reactions and to enable the self-saturating surface reactions. Typically, one of the precursors self-limitingly adsorbs largely intact, without thermal decomposition, while one of the precursors strips or replaces the ligands of the adsorbed layer. Surplus source chemicals and reaction by-products, if any, are removed from the reaction chamber by purging with an inert gas and/or evacuating the chamber before the next reactive chemical pulse is introduced. ALD provides controlled film growth as well as outstanding conformality. Various ALD recipes are possible with different reactants supplied in sequential pulses each with different functions, but the hallmark of ALD is self-limiting deposition.
Metal containing cyclopentadienyl compounds are technologically very important and have a variety of industrially useful properties. One such property is the ability for these compounds to adhere to both metals and nonmetals. Furthermore, without being bound to any theory, it is believed that the attached cyclopentadienyl ligand(s) contribute to overall compound stability. As a result, metal containing compounds can be used, for example, as precursors for forming adhesion layers in various structures including semiconductors, insulators, and ferroelectrics.
Metal containing films have previously been manufactured by physical vapor deposition (PVD) methods. These processes are well-known in the art. However, the PVD process has a number of drawbacks. For example, the PVD process is difficult or impossible to use for depositing thin film layers on complicated surfaces such as microelectronic surfaces with deep trenches and holes. In contrast, ALD processes can provide films of uniform quality and thickness.
Several different metal containing precursors have been previously used in ALD methods, but these precursors have a tendency to incorporate impurities into the growing thin film. For example, known processes utilizing metal chlorides, such as TiCl4, and hydrogen plasma incorporate halide impurities into the resulting thin films. Similar concerns arise for known non-halide metal precursors such as metal containing alkoxides, like Ti(OMe)4, where oxygen tends to remain in the film as an impurity.
As an alternative to the halide and oxide precursors, metal alkylamides, have been used in the art as precursors for ALD processes. However, these compounds suffer from thermal instability such that it can be difficult to find a deposition temperature that will not cause decomposition of the precursors and will keep the thin film atoms intact, but will still keep the precursors in vapor phase and provide the activation energy for the surface reactions.
In one aspect of the invention, atomic layer deposition (ALD) processes for producing metal containing thin films are provided. The processes preferably comprise alternately contacting a substrate in a reaction space with vapor phase pulses of at least one metal containing cyclopentadienyl precursor and at least one second reactant, such that a thin metal-containing film is formed on the substrate. In some embodiments, the metal containing cyclopentadienyl precursor comprises a metal atom that is not directly bonded to a halide or oxygen atom. In further embodiments, the metal atom is bonded to at least one cyclopentadienyl ligand and separately bonded to at least one ligand via nitrogen, wherein the ligands may comprise oxygenated or halogenated groups not directly bonded to the metal. In other embodiments the cyclopentadienyl precursor does not contain halide or oxygen atoms at all. In yet other embodiments, the metal containing cyclopentadienyl precursor comprises a nitrogen-bridged ligand.
In preferred embodiments, the metal containing cyclopentadienyl precursor comprises a metal selected from the group consisting of Al, Ga, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, Tc, Ru, Rh, La, Hf, Ta, W, Re, Os, and Ir, more preferably from the group consisting of Ti, Zr, Hf, Ta, W, Nb, and Mo. In some embodiments, the metal containing cyclopentadienyl precursor comprises a metal with a trivalent oxidation state.
In another aspect of the invention, ALD processes for forming an elemental metal thin film are provided. The processes preferably comprise alternately contacting a substrate with a metal containing cyclopentadienyl precursor as described above and a second reactant such that an elemental metal thin film is formed on the substrate. In some embodiments, the second reactant is selected from hydrogen or hydrogen plasma. The cycles are repeated until a thin film of the desired thickness has been deposited.
In another aspect of the invention, ALD processes for forming a metal nitride thin film are provided. The processes preferably comprise alternately contacting a substrate with a metal containing cyclopentadienyl reactant as provided above and a second nitrogen containing reactant such that a metal nitride thin film is formed on the substrate. In some embodiments, the second reactant is selected from NH3, N2 plasma, N2/H2 plasma, hydrazine, and/or hydrazine derivatives.
In another aspect of the invention, an atomic layer deposition process for forming a metal carbide thin film comprises alternately contacting a substrate with a metal containing cyclopentadienyl precursor as provided above and second carbon containing reactant such that a metal carbide thin film is formed on the substrate. In some embodiments, the carbon source is a hydrocarbon such as an alkane, alkene, and/or alkyne. In other embodiments, the carbon containing compound preferably comprises a central atom selected from group B, Al, Ga, In, Si, Ge, Sn, P, As, or S.
In another aspect, multicomponent thin films are deposited by atomic layer deposition processes. The processes preferably comprise at least two growth sub-cycles with the first sub-cycle comprising contacting a substrate with alternate and sequential vapor phase pulses of a first metal precursor and a first reactant, and then a second sub-cycle comprising contacting the substrate with alternate and sequential vapor phase pulses of a second metal precursor and a second reactant. In some embodiments the second metal precursor is different from the first metal precursor. For example, the second metal precursor may comprise a different metal from the first metal precursor. In other embodiments the second reactant is different from the first reactant. For example, the first and second reactants may contribute different species, such as N, C, or O to the growing film. In at least one of the growth sub-cycles the metal precursor is a metal containing cyclopentadienyl precursor as described above. The sub-cycles may be repeated in equivalent numbers. However, in some embodiments the ratio of the sub-cycles is varied to achieve the desired film composition, as will be apparent to the skilled artisan.
In another aspect, a multicomponent thin film comprises at least one elemental metal layer whereby at least one of the growth sub-cycles comprises contacting a substrate with alternate and sequential vapor phase pulses of a metal containing cyclopentadienyl precursor and a reactant. In some embodiments, the reactant is selected from hydrogen and hydrogen plasma.
In another aspect, a multicomponent thin film comprising at least one metal nitride layer is deposited by atomic layer deposition type processes. The processes preferably comprise at least one sub-cycle of alternating and sequential pulses of a metal containing cyclopentadienyl precursor and a nitrogen containing reactant. In some embodiments the nitrogen containing material is selected from the group consisting of NH3, N2 plasma, N2/H2 plasma, hydrazine, and hydrazine derivatives.
In another aspect, a multicomponent thin film comprising at least one metal carbide layer is deposited by atomic layer deposition type processes. The processes preferably comprise at least one sub-cycle of alternating and sequential pulses of a metal containing cyclopentadienyl precursor and a carbon source material. In some embodiments the carbon source material is a hydrocarbon. In other embodiments, the hydrocarbon is selected from alkanes, alkenes, and alkynes. The carbon containing compound may be one with a central atom selected from group B, Al, Ga, In, Si, Ge, Sn, P, As, or S.
The disclosed ALD processes preferably comprise at least one sub-cycle comprising alternating and sequential pulses of a metal containing cyclopentadienyl precursor. Preferably, the metal containing cyclopentadienyl precursor comprises at least one cyclopentadienyl ligand and a metal that is not directly bonded to a halide or oxygen atom. Alternatively, the metal precursor comprises at least one cyclopentadienyl ligand and at least one ligand that is separately bonded to the metal via nitrogen, wherein each ligand may contain oxygenated or halogenated groups not directly bonded to the metal. In some preferable embodiments, at least one chelating ligand, such as a bidentate ligand, is bonded to the metal via nitrogen. Additionally, the metal containing cyclopentadienyl precursor may comprise a nitrogen-bridged ligand. In some embodiments the precursor does not comprise any oxygen or halide atoms.
Preferably, the metal precursor is selected from (R1R2R3R4R5 Cp)x-MR0z—(R6)y, R1R2R3R4R5Cp)x-MR0z—(NR1R2)y, (R1R2R3R4R5Cp)x-MR0z—(NR1NR2R)y, and (R1R2R3R4R5Cp)x-MR0z—[(NR1NR2)CNR3]y, (R1R2R3R4R5Cp)x-MR0z—[(NR1NR2)CNR3R4]y. The metal containing cyclopentadienyl precursor may be, for example, a titanium cyclopentadienyl compound having the formulas described. In some embodiments the precursor is biscyclopentadienyl triisopropylguanidinato titanium (III).
Preferably the substrate temperature is higher than the evaporation temperature of the precursor and lower than the decomposition temperature of the precursor.